This invention is directed broadly to mercury vapor arc discharge lamps and more particularly to methods for avoidance of soluble mercury pollution of landfills and groundwater upon disposal of such lamps and during TCLP testing for leaching of soluble mercury materials from such lamps. Compositions of matter useful in preventing the formation of leachable mercury in disposal and testing procedures form a part of the invention.
Low pressure mercury arc discharge lamps are standard lighting means which include electrodes sealed in a glass envelope, the interior of which may be coated with a phosphor. The lamp also contains a small amount of mercury and an inert gas at low pressure, of about 1 to 5 torr. The term lamp, as used herein, means the complete unit including the glass envelope and the end pieces and plugs for mounting in a lamp fixture, and wires which connect the internal components of the envelope with the end pieces.
During manufacture of fluorescent or low pressure mercury arc lamps an amount of elemental mercury (Hg.sup.0) is sealed in the lamp envelope. Most of the mercury adheres to the phosphor coating, a small amount being in the vapor phase.
During operation, alkali metal carbonates from the electrodes decompose and form free oxygen in the lamp. The oxygen may react with a portion of the mercury to form soluble mercury oxide (HgO). Soluble mercury oxide is leachable from land fills and other disposal facilities. Soluble mercury oxides or other oxidized forms of mercury formed in the course of the test are detrimental to the accuracy and reliability of the standard test for determination of the leachability of toxic materials from lamp waste. This test is generally referred to as the Toxicity Leaching Characteristic Procedure or TLCP test.
There is concern about the environmental impact of soluble mercury compounds which can leach into ground water sources, rivers, streams, and the like. The lamps provided by this invention are characterized by low levels of leachable mercury when the lamp is pulverized for testing or upon disposal in a landfill.
In the prior art, certain oxidants and reductants are placed in a lamp to alter the form of mercury in the course of the TCLP test. These agents function to remove leachable mercury from the TCLP solution. The method of the instant invention prevents formation of leachable mercury and also reduce any leached or soluble mercury to insoluble elemental mercury. The dehydroascorbic acid antioxidant of this invention prevents oxidation of iron and copper, thereby preventing formation of leachable mercury, and also reduces oxidized or soluble mercury. This later capability lessens mercury contamination within a landfill. Reduction of soluble mercury to insoluble elemental mercury also provides a method for recovery of mercury from contaminated soil and water.